The present invention relates to plain bearings using aluminium based alloys as the bearing materials, for example for use in medium speed diesel engines.
Medium speed diesel engine connecting rod and main bearings, using a lining material of AlSn20Cu1 were originally produced without an overlay. However, in some instances these engines could be assembled with more in-built dirt than could be tolerated by the lining alone. This resulted in early seizure. The solution to the problem was to overlay plate the AlSn20Cu1 with lead/tin or lead/tin/copper, using a nickel interlayer.
For many years, bearings incorporating a nickel interlayer were extremely satisfactory. However, in recent years, particularly with the increased use of lower and lower quality residual fuel oils, overlay life in many engines has been drastically reduced due to a combination of corrosion and abrasion. The result of this is that relatively large areas of nickel interlayer can be exposed in a relatively short time. There is very strong circumstantial evidence to suggest that this exposed nickel at some stage becomes harmful and can inhibit further satisfactory bearing operation and may result in seizure.